NCERT Gist: Acids,Bases And Salts | Additional Study Material for UPSC PDF Download

- Curd, lemon juice, orange juice and vinegar taste sour. These substances taste sour because they contain acids.
- The chemical nature of such substances is acidic. The word acid comes from the Latin word acere which means sour.
- The acids in these substances are natural acids.
- Baking Soda- it does not taste sour it means, that it has no acids in it. It is bitter in taste.
- If you rub its solution between fingers, it feels soapy.
- Substances like these which are bitter in taste and feel soapy on touching are known as bases. The nature of such substances is said to be basic.
- Special types of substances are used to test whether a substance is acidic or basic. These substances are known as indicators.
- The indicators change their colour when added to a solution containing an acidic or a basic substance.
- Turmeric, litmus, China rose petals (Gudhal), etc., are some of the naturally occurring indicators.
- Name of acid Found
(a) Acetic acid — Vinegar
(b) Formic acid — Ant’s sting
(c) Citric acid — Citrus fruits such as oranges, lemons, etc.
(d) Lactic acid — Curd
(e) Oxalic acid — Spinach
(f) Ascorbic acid — Amla, Citrus fruits (Vitamin C)
(g) Tartaric acid — Tamarind, grapes, unripe mangoes, etc.
- All the acids mentioned above occur in nature Name of base Found in Calcium hydroxide
- Lime water Ammonium hydroxide Window cleaner Sodium hydroxide/ Soap Potassium hydroxide Magnesium hydroxide Milk of magnesia.
- The most commonly used natural indicator is litmus. It is extracted from lichens. It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper, known as litmus paper. Generally, it is available as red and blue litmus paper.
- The solutions which do not change the colour of either red or blue litmus are known as neutral solutions.
- These substances are neither acidic nor basic.
- Turmeric is another natural indicator.
- China Rose as Indicator turns acidic solutions to dark pink (magenta) and basic solutions to green.
- The rain containing excess of acids is called an acid rain.
- The rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide (which are released into the air as pollutants) dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively.
- Acid rain can cause damage to buildings, historical monuments, plants and animals.
- It is evident that when the solution is basic, phenolphthalein gives a pink colour. On the other hand, when the solution is acidic, it remains colourless.
- When an acidic solution is mixed with a basic solution, both the solutions neutralise the effect of each other.
- When an acid solution and a base solution are mixed in suitable amounts, both the acidic nature of the acid and the basic nature of the base are destroyed.
- The resulting solution is neither acidic nor basic.
- In neutralisation reaction, heat is always produced, or evolved.
- The evolved heat raises the temperature of the reaction mixture.
- In neutralisation reaction a new substance is formed. This is called salt.
- Salt may be acidic, basic or neutral in nature.
- The reaction between an acid and a base is known as neutralisation.
- Salt and water are produced in this process with the evolution of heat.
- Stomach contains hydrochloric acid. It helps us to digest food.
- When an ant bites, it injects the acidic liquid (formic acid) into the skin.
- The effect of the acid can be neutralized by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.